The various rails in use are distinguished by their weight
expressed in pounds per yard and by the section to which they are rolled. The rail
section which finds almost universal acceptance today is the "T" section or
flat-bottomed rail. It is designed as a girder to distribute a wheel load over several
adjacent sleepers and is the development resulting from earlier failures and
weaknesses.

Prior to 1905 no uniformity of rail section had been adopted by the Department and
rails were rolled or purchased as seemed convenient and suitable to meet its
requirements. These were produced in 40 lb., 53 lb., 56 Ib., and 70 lb. to the yard.
Sometimes, these rails, though produced in England, were rolled to American rail
sections. In 1905 the first British Standard rail designs were published, and at that
date the Department adopted the British Standard sections and these remained in use
until about 1930. The weights used during this period were 55 Ib., 70 Ib., and 100 Ib.
These rails are known to the track staff as "Old British Standard" or simply as
"O.B.S." rails.

In 1924 the 1905 standard rail sections were redesigned generally increasing the height
whilst leaving the width of base unaltered. The weights of these sections used by the
Department were 70 lb., 75lb., 85 lb., and 100 Ib. It is now the practice by track
staff to designate the rails rolled to the 1924 standard as "New British Standard" or
"N.B.S.". Officially, they are known as "Revised British Standard" or "R.B.S." rails,
and are distinguished by the letter "R " following the weight on the rail brand, thus
-70 R. No further bulk supplies of these rails will be purchased.

As a war emergency measure quantity of 75 lb. and 90 lb. rails to standard American
designs were imported.

In 1950, following upon the discovery of certain weaknesses in the British Standard
sections and the necessity for a slightly heavier rail, the Department prepared its
own designs for two new weights and designated these 72 1b, N.Z.R. and 91 1b. N.Z.R.

It may be said, generally, that the length of rails has increased proportionately to
the increase in weight with an upper limit of 42 ft. for all standardised rails from
70 lb. to 91 lb. Green ends -shorter rails for use in laying the low legs of curves
-are usually in lengths of 41 ft. 81/2 in. for 70 lb., and 41 ft. 71/2 in. for 85 lb.,
91 lb., and 100 lb.

?? Steel Co 5501 1900 Kaiwharawhara overbridge structure. The manufacturer may have been National Steel (from a list compiled by J A Dangerfield).

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1908 Barrier, Hutt Shops Elizabeth St

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1916 Epuni Verandah

NZR BS 70 D L & Co Ltd P G 7/1925 Guard rail on Ava Bridge, up main. Bessemer Steel 70 lb/yd, Dorman Long & Co. There is no "R" after the weight so this is Old British Standard (OBS) rolled to a 1905 specification.